Create switch for using data sources

Make it easy to use/ignore data sources in police project so we can learn how useful each is. That helps us build better models and it helps our partners understand why we're asking for dataset X (and what they lose when they don't share it)

Start by locating where the police project selects and loads data sources, then determine how model training currently includes them. Done means users can switch individual sources on or off and compare the resulting models, with the impact of omitted datasets clear to partners.

Written by the indexing model from the issue text.